1. Field of the Invention
This invention relates, generally, to techniques for the repair of the lower units of inboard or outboard motors. More particularly, it relates to a repair method that eliminates the practice of discarding lower units having worn screw threads.
2. Description of the Prior Art
Motorboat lower units are large, monolithic structures that depend downwardly from the hull of a boat at the trailing end thereof. More specifically, a lower unit includes a vertical strut that depends from an upper part of the lower unit, and a generally cylindrical housing is formed integrally with said vertical strut, about mid-length thereof. The propeller and related parts, such as bearings, are mounted to the trailing end of the generally cylindrical housing. The trailing end of the housing is open and cylindrical in configuration, and internal screw threads are formed therein, together with a plurality of circular cavitation grooves. More particularly, the cavitation grooves are formed in the trailing end of the housing, and the screw threads are formed adjacent said grooves, on the leading side thereof. A propeller housing having external screw threads formed thereon screw-threadedly engages the internal screw threads of the generally cylindrical housing when the lower unit is fully assembled. The cavitation grooves are not engaged.
The leading part of the generally cylindrical housing is tapered downwardly, i.e., its diameter decreases in a trailing-to-leading direction, and the leading end of said housing is closed.
The screw threads formed in the trailing end of the cylindrical housing eventually become worn because of the deleterious environment within which the lower units are used. Due to the monolithic nature of the lower unit, and due to the absence of any obvious way to repair the worn threads, the conventional practice is to discard the entire lower unit when said threads are worn. A new lower unit must then be purchased by the boat owner. Thus, lower unit worn threads represent a rather catastrophic expense to the boat owner, but those of ordinary skill in this art have been unable to develop any repair techniques that would obviate the need to replace the unit in its entirety.